Numerical studies on the effects of water presence in the coal matrix and coal shrinkage and swelling phenomena on CO&lt;SUB align= �right �&gt;2-enhanced coalbed methane recovery process

Thararoop, Prob; Karpyn, Zuleima T.; Ertekin, Turgay

doi:10.1504/ijogct.2012.044177

Cited by 6 publications

(4 citation statements)

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“…Moreover, the existing oxygen-containing functional groups are preferentially occupied by the adsorbed water molecules . Through long-term research, researchers have found that the existence of water can diminish gas (e.g., CH 4 , CO 2 ) adsorption, diffusion, and seepage capacities of coal. , Based on this, to effectively control gas disasters or improve the CBM recovery rate, a variety of technologies have been proposed to regulate the coal–water interactions of in situ coal seams. − Unfortunately, the fundamental understanding of the pore characteristics of coal-containing water and the relations with gas occurrence and migration capacities are still unclear.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Chen

Zhang

et al. 2022

ACS Omega

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Coal–water interactions have a prominent impact on the prediction of coal mine gas disasters and coalbed methane extraction. The change of characteristics in the microscopic pores of coal caused by the existence of water is an important factor affecting the diffusion and migration of gas in coal. The low-pressure nitrogen adsorption experiments and gas desorption experiments of a low-rank coal with different equilibrium moisture contents were conducted. The results show that both the specific surface area and pore volume decrease significantly as the moisture content increases, and the micropores (pore diameter <10 nm) are most affected by the water adsorbed by coal. In particular, for a water-equilibrated coal sample at 98% relative humidity, micropores with pore sizes smaller than 4 nm as determined by the density functional theory model almost disappear, probably due to the blocking effects of water clusters and capillary water. In this case, micropores with a diameter less than 10 nm still contribute most of the specific surface area for gas adsorption in coal. Furthermore, the fractal dimensions at relative pressures of 0–0.5 (D 1) and 0.5–1 (D 2) calculated by the Frenkel–Halsey–Hill model indicate that when the moisture content is less than 4.74%, D 1 decreases rapidly, whereas D 2 shows a slight reduction as the moisture content increased. In contrast, when the moisture content exceeds 4.74%, further increases in the moisture content cause D 2 to decrease significantly, while there is nearly no change for D 1. The correlation analyses show that the ultimate desorption volume and initial desorption rate are closely related to the fractal dimension D 1, while the desorption constant (K t) mainly depends on the fractal dimension D 2. Therefore, the gas desorption performances of coal have a close association with the pore properties of coal under water-containing conditions, which indicate that the fluctuation in moisture content should be carefully considered in the evaluation of gas diffusion and migration performances of in situ coal seams.

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Section: Introductionmentioning

confidence: 99%

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Chen

Zhang

et al. 2022

ACS Omega

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“…Equilibrium was reached in this case depending on water pressure, length, and the inner diameter of the tube. The relationship between water injection and gas pressures conforms to Equation (1) [35,36] as…”

Section: Theoretical Studymentioning

confidence: 96%

Methane Desorption Characteristics of Coal at Different Water Injection Pressures Based on Pore Size Distribution Law

Zhao¹,

Gao

et al. 2018

Energies

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Methane desorption characteristics of coal under definite water pressure comprises a complex two-phase flow process. A series of mercury intrusion porosimetry (MIP) and desorption experiments at different water injection pressures are reported in this study. Three lumpy coal samples were used in desorption experiments at three different water injection pressures and at natural desorption for comparison. Samples comprising two ranks of coal were used for MIP measurements including the distribution of porosity and pore sizes. The results of this study enable the establishment of a new model that encompasses a critical theoretical pore size that is most effective for water injection into coalbeds and that can be related to water injection pressure, the length of residual water, and gas adsorption capacity. Data show that the use of different water injection pressures leads to different gas desorption capacities as well as variable time effects and degree of gas desorption. Critical pore size is therefore proposed as a new parameter that can be employed to describe high pressure water effects in the context of gas desorption and can be calculated using pore size and the volume distribution law, as well as via the moisture ratio that remains after experiments and the permanent desorption percentage.

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“…First, some scholars studied the presence of water in coal and the characteristics of methane transport law and discussed to derive the gas transport law and stress changes in coal caused by the water movement. It was shown that the water–methane repulsion effect objectively exists; free methane can be produced by competitive adsorption and replacement desorption of methane and water. − According to the mechanism of the influence of water on the methane adsorption properties of coal, coal seam water injection for mining has become an important tool in engineering practice. Pu conducted a series of experiments to study the differences in mechanical property changes under wetting conditions with different coal samples.…”

Section: Introductionmentioning

confidence: 99%

Effect of Different Placement Sequences of Water on the Methane Adsorption Properties of Coal

et al. 2023

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After the coal seam is injected with water, the moisture content in the coal body increases, which affects the output capacity of coalbed methane (CBM). In order to improve the effect of CBM mining, the classical anthracite molecular model has been selected. To analyze the influence of different placement orders of water and methane on the characteristics of coal-adsorbing methane from the micro point of view, a molecular simulation method is used for comprehensive consideration in the study. The results show that H2O does not change the mechanism of CH4 adsorption by anthracite, but it inhibits the adsorption of methane by anthracite. When water enters the system afterward, there arises an equilibrium pressure point where water plays the most significant role in inhibiting methane adsorption by anthracite coals, which increases with increasing moisture content. When water enters the system first, no equilibrium pressure point occurs. The excess adsorption of methane by anthracite when water enters second is higher. The reason is that H2O can replace CH4 at the higher energy adsorption sites of the anthracite structure, while CH4 can only be adsorbed at the lower energy sites, and some of CH4 is not adsorbed. For the coal samples with a low-moisture content system, the equivalent heat of adsorption of CH4 increases first rapidly and then slowly with the increase of pressure. However, it decreases with pressure in the high-moisture content system. The variation of the equivalent heat of adsorption further explains the variation of the magnitude of methane adsorption under different conditions.

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Numerical studies on the effects of water presence in the coal matrix and coal shrinkage and swelling phenomena on CO<SUB align= �right �>2-enhanced coalbed methane recovery process

Cited by 6 publications

References 0 publications

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Methane Desorption Characteristics of Coal at Different Water Injection Pressures Based on Pore Size Distribution Law

Effect of Different Placement Sequences of Water on the Methane Adsorption Properties of Coal

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